Regulating means for high power electric discharge amplifiers



March 21, 1933. D. ANDREWS 1,902,484

REQULATING MEANSFOR HIGH rowan ELECTRIC DISCHARGE AMPLIFIERS Filed April 12, 1930 Inventor: Paul D. Andrews,

' His Attornqg.

Patented Mar. 21, 1933 a '1 I 1 UNITED STATES PATENT OFFICE rAnL 15. Annnnws, or scnnivno'ranr, NEW Yonir, nssre voa 'ro enivnnnnntncrarc f coMrAnmn CORPORATION on NEW Yoax REGULATING MEANS FOR HIGH POWER ELECTRIC DISCHARGE AMPLIFIERS I Application filed April 12, 1930; Serial No. 44 3,876; V V i The present invention relates to means for additional grid of tubes such as the four-ele-. regulating electric discharge amplifiers and ment type in any amplifier circuit. .Such more particularly, it relates to means for tubes, as is well understood, are provided regulating amplifiers employing multi-grid with a grid between the cathode and the 5 electric discharge devices arranged to transanode and another grid between the ifi'rst 55? mit relatively large amounts of energy such named gridand the anode. One suchm'ethod as are employed in radio transmitter circuits comprises applying directly to the additional and the like. grid, whether it be the one adjacent. the

High power amplifiers :of this character cathode or the second named grid, a suitable having multi-grid amplifier devicesare pro- VD. Crbiasing voltage fromza generator or vided with positive biasing voltages which biasingbattery-source, an average voltage are applied to the additional gridsof the value beingselected in ordertoprovi-defthe tubes for the purpose of controlling the opbest average operating condition over the crating characteristics. The exact amount" various conditions under ,wh-ich'thetube, is" v of positive biasing voltage which is supplied required to operate; Asignal or A. C. coni to the additional grid in a multi-grid. tube trolpotential maybe applied to the other: or electric discharge device, varies with grid. v r g different types of tubes and also with different As is well known, normal'screengrid op} 7 applications of the same type of tube, but eration is had when the signal is applied to this voltage is ordinarily approximately 20 to the first or normal control grid and space 793 per cent of the D. Caplate'voltage used charge gridoperation is had when the signal with a tube of the four-element type inthat isapplied to thesecond gri-d,the positive biasparticular application. w ing potential being applied in each case to.

0 If the positive biasing voltage applied to the remaining grid. g v

the additional grid is too low in value, the With thedirect application of a positive impedance of the tube under operating condibiasing voltage to the additional grid,jit has tions will be too high for eflicient operation been found that under certain ope-rating conand the amplification realized from the tube ditions the tube tends to drawaheavy' plate 30 will be small. If, however, this positive biascurrent, and that as a result, the D. C. current f grid or space charge grid, as the case may to a very I WYaI e an m y (W611v m be, will tend to overheat and to draw too high reversed. 1 V I a current from the biasing source. This con- In general, it may be saidthat in the opstitutes an unnecessary drain on the electron 1 eration of an amplifier including a" multiemission of the tube filaments and if congrid electric discharge device such'asa foursiderable overheating of the additional grid element tube, with apositive biasing poten-. takes place, it may'also result in liberating tial applied to the additionad grid directly. possible gases from the material constituting from a source of potential, as the-D. G. plate this additional grid. current drawnby the tube decreases, the cor- In, extreme cases, the additional grid may responding D. C. currentdrawn'by the adeven become so hot as tovbecome fused and ditional grid'will tend'to increase almostin' permanently damaged. This is particularly proportion. In such a case, it will frequently true in transmitting circuits where relatively be found that the energy dissipated from the A: large amounts of power are controlled by the additional grid in the tube will be excessive tubes. Hence, the control of the biasing and will result .in'seriously overheating this voltage for the additional grids of amplifiers grid. i employing multi-grid electric discharge 'de- It is for the above reasons that another vices is important.

. method of operating a multi-grid electric 6 Several methods are in use for obtaining discharge device such as a screen grid or 100 the necessary positlve blasing voltage for the space charge grid tube in an amplifier has ing voltage is too high in value, the screen drawn by the additional grid will decrease I been followed to a greater extent and is used so that under various conditions of operation thepotential applied to this grid is still always sufficiently high to-cause the current drawn by this grid to flow in the proper direction.

While this arrangement has the advan-' tage that the lower the current drawn by the additional gridtends to become, the higher the positive biasing potential applied to the grid will become, it is inherently inefiicieut in that a higher value of supply voltage is required and a considerable energy loss must at all times occur in-the series resistor used;

For use in power amplifier circuitsfor transmitters and the like the series resistor mustnecessarily be of a high value, for example.

in the order of 50,000 ohms, anda resistor of the value when required to dissipate any appreciable energy is'somewhatof a problem.

In view of the disadvantages of the direct method of applying a required operating voltage to a grid of a multi-grid electric discharge device such as that of the type .above described, and of the series resistance type of control ofs'uch voltage, it is the object of the present invention to provide an improved method of applying a biasing potential or voltage to a grid of a multi-grid electric discharge device for the purpose ofregulating an amplifier in which said 'device is included, and an improved circuit control means for efl'ecting such regulation. The invention will be better understood from the following description when taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing. the figure is a schematic wiring diagram of an amplifier stage including a multi-grid electric discharge device provided with a regulating "means embodying the invention.

Referringto the drawing, 5 is an electric discharge device of the four-element type having a hot cathode 6, a control electrode or grid 7, an anode 8 and an additional. grid 9. By way of example,this is type of electric discharge device commonly known as a screen grid tube in which grid 9 is adjacent the anode and 1s employed as a biasing electrode, while grid 7 is the normal control electrode. It serves to illustrate any multigrid electric discharge device having a grid which requires a controlled current at a predetermined range of applied potential.

Thetube is included in an amplifier circult provided with an input c1rcu1t 1nd1- eated at 10 and an output circuit indicated at 11. The input circuit is connected with the controlgrid 7 and includes a grid-lead reactor 12 and a grid-leak resistor 13 to which is applieda suitable negative biasing potential or voltageas indicated at 14. An

alternating current input control voltage is applied to grid 7 and the input circuit 10 throughta coupling capacitor 15 and an input lead16.. The input'lead 16 may be connected toany suitable source (not shown) of controlling or excitation alternating cur:

rent potential for the amplifier stage.

The output circuit 11 is connected with the anode 8 and includesa tuning inductance 17 and a tuning capacitor 18 in shunt therewith, together with a suitable by-pass capacitore. 19 connected between the low potential endof the output, circuit 11, as indicated at 20, and a cathode return lead 21 which is grounded, asindicated at 22.

Inductance 17' and tuning capacitor 18 constitute a tuned circuit from the high potential end of which output alternating currentenergy from the amplifier may be takenthrough a suitable coupling capacitor 23 and anoutput lead 24 connected therewith. The by-pass capacitor 19 serves to maintain one endof the tuned anode'circuit at ground or filament potential with respect'to the audio or radio frequency current which traverses;

the output circuit. A positive operating voltageforthe anode or output circuit 11-is supplied thereto through a suitable. supply lead 25 to which a positive operating potential is applied, as indicated at 26'.

In accordance with the invention, apositive biasing potential is applied to the additional grid or the grid requiring an applied operating potential, which in the present example is grid 9, through a supply lead 27 from asupply source of positive biasing potential as indicated at 28. Supply lead 27-- is suitably by-passed adjacent grid 9 by a capacitor 29 connected between said lead and the cathode return lead 21, asindicated. Capacitor 29 is so selected that it possesses a low reactance atthe operating frequency of the amplifier stage and serves to maintain the additional gridat ground or cathode potential' as regards any A. C. potential.

Insertedin supply lead 27 is a regulating or control device 30 which provides a series regulating resistance in the positive biasing circuit; The resistance characteristic of the device 30 is such that it does notmaintain a constant value, when a'varying current flows therethrough, but automatically varies in re par sistance value in accordance with the various operating conditions which may tend to effect adverse changes in the applied potential on grid 9, to provide an optimum operating condition for the tube. In other words, its resistance value'varies in response to changes in the current flow through it, and may be considered to be of the ballast type which tends to maintain through ita current which varies between relatively narrow and safe limits.

' Such an automatically regulating resistance is easily applied to any supply voltage circuit forjan additional grid in an amplifier stageby merely inserting such-a device in circuit therewith; It does not, -therefore,require further changes in the circuit than are necessary for the use of the ordinary series resistance hereinbeforementioned, which has operating disadvantages hereinbefore described.

adapted for the automatic control of the biasing voltage for the additional grid of an amplifier device of the above type. It is ob-, vious that'any de'siredvalue of regulating resistance maybythis means be provided by providing the proper size of lamp or by properly combiningthe filaments of two or more lamps in series parallel relation.

It will readily be seen that as the current drawn by the additional or bias potential grid of the tube tends to become excessively high, the resistance of the series control device 30 becomes rapidly higher and easily prevents this current from reaching an excessive value. On the other hand, asthe cur-j rent drawn by the additional grid would i tend'to become very low under certain operating conditions, the resistance of'the series regulating device becomes lower and lower thereby tending to maintain the current more constant thanwould an ordinary resistor, and consequently the voltage applied to the additional grid is increased while at all times the energy loss in the control device is automatically maintained at a minimum value.

Assuming that the positive biasing voltage applied to the additional grid has been properly selected initially, it is then readily possible to establish an operating condition under which the current drawn by the additional grid will never reverse and also will never reach an excessively high condition.

Thus, it is at once evident that this method of obtaining the positive biasing voltage for a the additional grid in, an amplifier tube of this character provides more favorableop-J crating conditions than either of the known methodsrhereinbefore described- Instead of employing a filament of astaiidard incandescent lamp or a plurality of such I lamps in series. parallel arrangement, asoine} what greater regulating characteristic maybe obtained by employing the filament. .of'

one of the so-called ballast or constant cur-1 rent type of lamps. As is well known, the

filament of the latter type of lampoperates generally in a gas filled bulb and provides a still greater resistance variation as the cure Any suitable resistance or resistor unit or device may, however be used which unit or device possesses the desired. feature of automatically varying its resistance value dependent upon and in accordancewith thecurrent passing through it. I 1 It will be seen that theabove-described method of applying an automatically adjustable'positive biasing voltage or potential to the additional grid in a four-element am plifier tube, for example, may apply equally well to either the screen grid or to thespace charge grid'type of tube, and that the'tube may be operated as either an audio or a radio frequency oscillator or amplifier, or in any other capacity to which such made tube may be applied.

It willbe appreciated that if a reverse-regulating action to that described in the foregoing is found desirable in certainspe'cial applications, the same may readily be obtained by substituting for a regulating de-- vice having a positive resistance characteris tic, such as that described, a regulating resistance having a negative coefiicient of -resistance. Such a device is fouiid'in a lamp of the carbon filament type, fer example. "In eitner case, however, the grid of the tube which is supplied with a positive biasing volt age receives a current at a voltage controlled by a device which in itself is'automatically adjustable in accordance with a tendency'o the current to increase or decrease.

From the foregoing description it will be] seen that with means for applying a positive biasing potential to a grid of a multi-grid electric discharge device, the disadvantages accompanying former methods are obviated. For example, if the tube tends to draw a crease or to become reversed, this actionis prevented by the rapidly increasing ap sistanceof the regulating device rapidlyde creases with decreased current'fiow. Likeli cation ofv voltage from the source as the res wise, as the D. C. plate currentdrawn by the tube decreases and the corresponding D. C. current drawn by the additional grid tends to increase almost in proportion as in the usual case, the energy dissipated by the additional grid under such operating conditions will be prevented from becoming excessive and from overheating the grid by the rapidly increasing value of the resistance of the regulating device as the current tends to increase. v The life of the tube is therefore greatly prolonged and operating conditions are improved.

It will further be seen that a regulating systemembodying the invention obviates the inefficiency accompanying the use of an ordinary series resistor of the type hereinbefore mentioned and prevents the excessive loss of energy which occurs in such a series resistor. As the resistance of the regulating device is automatically variable, it is required to dissipate only as much energy as is necessary to effect regulation. Furthermore, an excessively high and dangerous positive potential is prevented from being applied to the grid when such tube is cut ofi. as may occur during the telegraphic keying of an amplifier stage such as that of the present example.

What I claim as new anddesire to secure by Letters Patent of the United States is:

1. The combination with an electric discharge device having a control grid, a cathode, an anode, and an additional grid, of means for applying a positive biasing potential to said additional grid, said means including a voltage supply circuit and a constant current device in series with said supply circuit.

2. The combination with an electric dis charge device having a control grid, a cathode, an anode, and an additional grid, of means for applying a positive biasing potential to said additional grid, said means including a voltage supply circuit and a regulating device in series with said supply circuit, the resistance of which device automatically varies sufliciently in accordance with the flow of current through it to cause said biasing potential applied to said additional grid to be maintained within a predetermined desired range.

3. The combination with a multi-grid electric discharge device, of means for automatically applying a positive biasing potential to a grid thereof, said means including a supply lead adapted to be connected to a source of positive potential, and a regulating device connected in said supply lead, said device having a positive coefficient of resistance, whereby as the current flowing to said grid increases, the resistance of said device increases in proportion thereto.

4. The combination with an electric discharge device having a control grid and an additional grid, of means for applying a positive biasing potential tov said" additional grid, said means including a supply circuitand a regulating device connected in series therewith, said regulating device being of the ballast lamp type whereby its resistance varies in accordance with current flow therethrough.

'5. The combination with an electric discharge device having a cathode, an anode, a control electrode, and an additional electrode requiring the application of an optimum value of positive biasing voltage thereto for the normal operation of said device, of a lead for supplying a biasing potential to said additional electrode, and a regulating device connected in .said supply lead, said device having a resistance value which variesin dependence upon the current flowing through it. 7 6. The combination Withan electric discharge device having a cathode, an anode, a control electrode, and an additional electrode requiring the application of an optimum value of positive biasing voltage thereto for the normal operation of said device, of an input circuitconnected with the control electrode, ,a tuned output circuit connected withthe anode, a by-pass capacitor providing a connection between thelow potential end or" said output circuit and the cathode, a lead for supplying a biasing potential to said additional electrode, a by;-

pass capacitor providing a connection between the additional elec'trode. and said cathode, and a regulating device connected in said supply lead, said device having a resistancev value which varies in, dependence upon the current flowing through it.

7. The combination with an electric. discharge device having a control grid, cathode, an anode, and an additional grid, of means for applyinga positive potential to said anode, andmeansfor applying a positive biasing potential to said additional grid including a supply lead connected to a source.

of positive potential and a regulating device connected in circuit with said supply lead, the potential applied to said regulating-device from said source being substantially less than the potential applied to said anod'e,the resistance of said device automatically varying sufiiciently in accordance with the flow of current therethrough to cause said biasing potential applied to said additional grid to be maintained within a predetermined desired range. I p

8.. The combination with an ele'ctricdischarge device having a control grid, a cathode, an anode, and an additional grid, of means forapplying a positive potential to said anode, and means for automatically applying a positive biasing potential to said additional grid including a supply lead connected to a source of positive potential and a regulating device connected in said supply lead, said regulating device having a positive coeffioient of resistance whereby as the current flowing to said additional grid increases the resistance of said device increases to prevent excessive current flow to said additional grid, the potential applied to said regulating device from said sourcebeing sub stantially less than the potential applied to said anode whereby the potential of said additional grid is limited to a safe value.

In Witness whereof, I have hereunto set my hand this 11th day of April, 1930.

i PAUL D. ANDREWS. 

